CODEWITHSUNDEEP
javadictionaryhashmap
Tatanan
Tatanan

Reputation: 207

Which Map class should I use?

In http://docs.oracle.com/javase/7/docs/api/java/util/Map.html I see 19 classes that implement the Map interface. Which one should I use? I want to map integers to integers. I would use Array but I see HashMap in many example, so I am thinking about:

Map<Integer, Integer> myMap = Collections.synchronizedMap(new HashMap<Integer, Integer>());

Basically I want to simulate the less strict arrays that I can find on other languages like PHP where I can asign any integer to any value without caring about fixed lengths or using lists.

Upvotes: 0

Views: 75

Answers (3)

lreeder
lreeder

Reputation: 12206

If you're not concerned about thread-safety, just use Hashmap<Integer, Integer>. If multiple threads will be accessing the map, then ConcurrentHashMap is probably your best choice. See thread safe map for java for more details.

Upvotes: 1

Brian Agnew
Brian Agnew

Reputation: 272217

Your simplest and most straightforward option is to use a HashMap<Integer, Integer>(). You don't have to worry about threading, or paying for any performance penalty whilst sorting (as you would with TreeMap) etc.

You also ask about threading. Note that HashMap itself isn't thread safe, and simultaneous operations on it will blow up (e.g. maps do internal state changes like resizing upon puts, and a simultaneous put will likely fail). So a ConcurrentHashMap will likely be required. However note that you may need to still synchronise around that object if you're performing multiple atomic operations e.g.

if (!map.contains(key)) {
   map.put(key, ...);
}

Upvotes: 1

RMachnik
RMachnik

Reputation: 3684

You can simply use HashMap or MultiHashMapref from apache, dependent on your project requirements. Synchronized collections from Collections.synchronized* are slower than normal collections. So basically if you will not use that collection in multithreading environment you should avoid synchronized collections for basuc one thread stuff because they are simply slower.

Upvotes: 1

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